I have a 1992 Corvette that has had a recent tuneup. New OPTI spark cap, Wires and Plugs. It still runs rough at Idyl. Seems to have a miss in one of the cylinders. It smooths out a bit at higher RPMs, Usually over 3000 RPM it runs smoother. Any idea on what the problem is?
Thanks
Bruce

 

Do you have any codes?

 

There were some codes before the tuneup and a sensor was replaced. The garage told me there wasn't any codes. The Service Engine Soon light comes on after you drive it about 30 minutes. Don't think there are any codes, but how would I check.
Thanks
Bruce

 

You can either jump the pins in the ALDL or take it to Autozone and they will scan it for free. Only takes a minute. If you have an SES light then you should have stored codes. I have a hunch that its going to be Opti spark again. You replaced the cap (the high voltage side) but I bet you have the optical pick up side (the piece against the motor)of the opti going out. I would have replaced the complete Optispark if I had the engine tore down when you did or had all the work done because the labor is the same just the parts are a little higher.If you have a miss at high RPM it usually means a bad cap but if you have a miss at idle and rough running its usually the optical side. See if you have codes 16 and/or 36. Those are bad. I bet the common shaft has been wobbling and have worn out the bearings in it. I hope I am wrong for your wallets sake and I am not being a harbinger of doom.

 

please make sure it was a reputable mechanic and he did it correctly, if you can check all of the plugwire connections by your self do it ,the only other possibility is opti going out[:@][:@][:@]

 

I was away for a few days but I finally got the Codes off of the car. The codes that are there now are:
Code 15
Code 43
Code 52
Code 63
Any help would be appreciated. The garage that worked on the car has a good reputation, however they don't have alot of experience with Corvettes.
My understanding is that Code 43 is a EST or ESC problem. What ever that is??? A low voltage???
Please help.
Thanks
Bruce

 

Hi Bruce, I'm no expert at this by no means, but I had a camaro once that had a misfire at idle and ran smoother at higher rpm, turned out I had a burnt valve. Now I'm not saying that you have the same problem, but before I started buying and replacing new parts, I would do a compression test on all eight cylinders, if for no other reason, to rule out that possibility.

 

Hi,
Thanks for the reply. The garage thought it might be the same thing. They did do a compression test and the compression was even on all 8 cylinders. Since the compression is even, a burnt valve has been ruled out.
The car has only around 50,000 miles on it. The water pump leaked into the OPTI cap and that is why it was replaced. The car has sat for quite a long while. Fuel injector cleaner has helped smooth out the roughness a little bit.
It was running very rough before the major Tuneup, OPTI cap, Plugs, Plug wires and Fuel injector cleaner. It is running alot smoother now, however it still has a bit of a miss. The miss is more noticeable at low RPMs or when the car has a bit of a load (ie going up a steep hill).
Any more suggestions?
Bruce

 

I guess the next thing I would do is try to determine which cylinder is doing the missing by pulling the plug wires off one at a time until I found the culprit. If you do find one, check and make sure you're getting a good spark at the plug. Keep in mind, just because you bought new parts doesn't meanone can't be bad. If you have a good spark at the plug, check the injector, make sure the connector is getting a good connection. You said the car sat up for a while, could be a partially clogged injector, or even a bad injector. You could take it and have the injectors cleaned, I'm not talking about the additives you buy at an auto parts store, take it to a reputable shop that can run the good stuff through them.

 

Here's a link that can give you some info on the codes you got.

http://www.corvettebuyers.com/c4vettes/ecm.htm